a) Field of the Invention
The present invention relates to a process for stabilizing dibenzylidenesorbitols and a composition thereof. More particularly, it relates to a process for stabilizing dibenzylidenesorbitols whereby the increase of benzaldehydes over time is suppressed, and to a dibenzylidenesorbitol composition.
b) Description of the Related Art
Dibenzylidenesorbitols, when blended in small amounts with polyolefin resins, particularly with polyethylene, polypropylene or copolymers composed primarily of these resins, have the effect of improving the transparency of the resins, and hence they are useful compounds as additives to the resins in the area of molding various containers which demand transparency. Further, they are useful compounds also as gelling agents for a variety of organic solvents.
However, dibenzylidenesorbitols are relatively insufficient in stability so that they sometimes eliminate benzaldehydes to give out a nasty smell during storage or processing and cause the molded articles to assume an aldehyde smell or a color, thus raising a large difficulty depending on the use of the molded articles and obstructing the increase of their demand.
Further, even when dibenzylidenesorbitols are so purified that the smell can not be detected, their decomposition takes place by the action of temperature, water, etc. during storage and hence has been responsible for the nasty smell.
To solve the above-described problems, the following processes have been studied and disclosed.
There are disclosed processes which comprise mixing a dibenzylidenesorbitol with a lower aliphatic alcohol or lower aliphatic ketone under heating in Japanese Patent Laid-Open Nos. 5165/1978 and 185287/1982 and processes which comprise treating it with hydroxylamine or phenylhydrazine in Japanese Patent Laid-Open Nos. 32791/1985 and 42385/1985. However, all of these processes merely remove benzaldehydes contained as impurities and do not improve the stability to the decomposition during storage.
Japanese Patent Laid-Open No. 4289/1987 discloses sorbitol derivative compositions improved in thermal stability which are formed by adding nonaromatic organic amines to sorbitol derivatives. However, in the field where the compositions are used as additives to resins to prepare food containers, it is concerned if the safety of the containers is obstructed by the amines.
Japanese Patent Laid-Open Nos. 21440/1982 and 126352/1989 disclose a composition formed by covering the surface of a solid powder of a dibenzylidenesorbitol or di-substituted-benzylidenesorbitol derivative with a saturated higher fatty acid such as behenic acid. Here, it is described that mere addition is less effective and hence the surface must be covered with a surfactant or the like. Therefore, the production process of the composition is complicated and moreover it is necessary to use a relatively large amount of the higher fatty acid, i.e., 5-50 parts by weight of a higher fatty acid for each 95-50 parts by weight of a dibenzylidenesorbitol.
In the processing of a polyolefin resin, it has generally been adopted to blend 0.1 part by weight of a metallic salt of a carboxylic acid, such as calcium stearate, with 100 parts by weight of the resin, but this process can not improve the smell given off from the molded articles when a dibenzylidenesorbitol is added to the resin so as to make them transparent.